The present invention pertains in general to a device for measuring the internal diameter of tubes, and in particular to measuring the caliber of the barrels of firearms. The device consisting essentially of a measuring head with radially acting calipers which are functionally connected to an axially movable, spring-tensioned rod that is in turn connected to a measuring and display unit.
A similar measuring device for measuring internal diameters, whose measuring head has a measuring transducer that is movable radially relative to the longitudinal axis of the measuring device, has been known from West German Patent No. 32,38,336 C2. The radial movement of the measuring transducer or calipers is transmitted to an axially movable rod which is in functional connection with a dial gage. The measuring rod is subject to the action of a spring.
West German Patent No. 31,03,819 A1 also discloses a similar instrument for measuring internal diameters. In this patent measuring tips are actuated by a mobile measuring system formed by a rod that is axially movable. The rod is subject to the action of a spring in this instrument as well and is in contact with the measuring tip of a dial gage. The radial movement of the measuring tips is transmitted to the measuring rod in an axial direction of movement and is reported to the measured value acquisition unit.
These prior-art conventional methods measure the internal diameter of tubes only after the tubes have been disassembled and the result can be strongly influenced by the person performing the measurement. Particularly disadvantageous is the fact that these prior-art measuring instruments are able to determine a dimension only at a defined measuring position determined in advance. Continuous measurement of the internal diameter of the tube at a plurality of points located at axially spaced locations from each other is impossible. However, measurement at a plurality of measuring points, located at axially spaced locations from each other, is of particularly great importance for measuring the caliber of firearm barrels. Another requirement is that such a firearm barrel must be measured in the installed state in a relatively rapid measuring operation even under extreme weather conditions, and the measurement should scarcely be influenced by the operating personnel.